Channel-sounding method using a plurality of antennas, and apparatus for same

ABSTRACT

The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and to an apparatus for transmitting an SRS in a multi-antenna system. The method comprises the steps of: acquiring specific information for discriminating a first antenna group and a second antenna group from among a plurality of antennas, wherein said first antenna group includes one or more antennas which are set to a turned-on state to perform communication with a base station, and said second antenna group includes one or more other antennas which are set to a turned-off state; transmitting an SRS to the base station if a predetermined condition is satisfied, under the condition that the second antenna group is set to the turned-off state; and setting the second antenna group to a turned-off state after the transmission of the SRS.

TECHNICAL FIELD

The present invention relates to a wireless communication system.Particularly, the present invention relates to a channel sounding methodusing a plurality of antennas and an apparatus for the same.

BACKGROUND ART

A 3rd Generation Partnership Project Long Term Evolution (3GPP LTE)communication system, which is an example of a mobile communicationsystem to which the present invention may be applied, will now bedescribed in brief.

FIG. 1 is a diagram schematically showing a network structure of anEvolved Universal Mobile Telecommunications System (E-UMTS) as anexemplary mobile communication system. The E-UMTS system has evolvedfrom the conventional UMTS system and basic standardization thereof iscurrently underway in the 3GPP. The E-UMTS may be generally referred toas a Long Term Evolution (LTE) system. For details of the technicalspecifications of the UMTS and E-UMTS, refer to Release 7 and Release 8of “3rd Generation Partnership Project; Technical Specification GroupRadio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE) 120, eNBs(or eNode Bs or base stations) 110 a and 110 b, and an Access Gateway(AG) which is located at an end of a network (E-UTRAN) and connected toan external network. The eNBs may simultaneously transmit multiple datastreams for a broadcast service, a multicast service, and/or a unicastservice.

One or more cells may exist per eNB. A cell is set to use one ofbandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a downlink oruplink transport service to several UEs. Different cells may be set toprovide different bandwidths. The eNB controls data transmission andreception for a plurality of UEs. The eNB transmits downlink schedulinginformation with respect to downlink data to notify a corresponding UEof a time/frequency domain in which data is to be transmitted, coding,data size, and Hybrid Automatic Repeat and reQuest (HARQ)-relatedinformation. In addition, the eNB transmits uplink schedulinginformation with respect to UL data to a corresponding UE to inform theUE of an available time/frequency domain, coding, data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A Core Network (CN) mayinclude the AG, a network node for user registration of the UE, and thelike. The AG manages mobility of a UE on a Tracking Area (TA) basis,wherein one TA includes a plurality of cells.

Although wireless communication technology has been developed up to LTEbased on Wideband Code Division Multiple Access (WCDMA), the demands andexpectations of users and providers continue to increase. In addition,since other wireless access technologies continue to be developed, newtechnology is required to secure competitiveness in the future. Forexample, decrease of cost per bit, increase of service availability,flexible use of a frequency band, simple structure, open interface, andsuitable power consumption by a UE are required. Recently,standardization of a new technology subsequent to LTE (Release 8/9) isin progress in the 3GPP. In this specification, the technology isreferred to as “LTE-Advanced” or “LTE-A” (Release 10 or beyond).

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies inproviding a channel sounding method using a plurality of antennas in awireless communication system and an apparatus for the same.

Objects of the present invention are not limited to those describedabove and other objects will be clearly understood by those skilled inthe art from the following description.

Technical Solution

In one aspect of the present invention, the object of the presentinvention can be achieved by providing a method for a User Equipment(UE) to transmit a Sounding Reference Signal (SRS) using a plurality ofantennas in a wireless communication system, the method includingacquiring specific information for discriminating between a firstantenna group and a second antenna group among the plurality ofantennas, the first antenna group including one or more antennas whichare set in a turn-on state for communication with an eNode B and thesecond antenna group including one or more other antennas which are setin a turn-off state, transmitting an SRS to the eNode B through thesecond antenna group when a preset condition is satisfied with thesecond antenna group being set in a turn-off state, and setting thesecond antenna group in a turn-off state after transmitting the SRS.

In another aspect of the present invention, provided herein is a UserEquipment (UE) including a plurality of antennas, a Radio Frequency (RF)unit configured to transmit and receive a wireless signal to and from aneNode B through the plurality of antennas, a memory for storinginformation transmitted and received to and from the eNode B and aparameter required for operation of the UE, and a processor connected tothe RF unit and the memory, the processor being configured to controlthe RF unit and the memory, the processor being configured to perform aSounding Reference Signal (SRS) transmission method including acquiringspecific information for discriminating between a first antenna groupand a second antenna group among the plurality of antennas, the firstantenna group including one or more antennas which are set in a turn-onstate for communication with the eNode B and the second antenna groupincluding one or more other antennas which are set in a turn-off state,transmitting an SRS to the eNode B through the second antenna group whena preset condition is satisfied with the second antenna group being setin a turn-off state, and setting the second antenna group in a turn-offstate after transmitting the SRS.

Here, the second antenna group may include antennas in which an AntennaGain Imbalance (AGI) has occurred.

Here, whether or not the specific condition may be satisfied isdetermined based on whether or not a first duration for transmitting theSRS has elapsed and the first duration may be set to be longer than asecond duration for SRS transmission through the first antenna group. Inthis case, the first duration may be set as a multiple of the secondduration.

Here, an SRS may be transmitted to the eNode B through all antennasprovided for the UE when the preset condition is satisfied.

Here, whether or not the specific condition is satisfied may bedetermined based on whether or not an SRS request for the second antennagroup has been received from the eNode B. In this case, the SRS requestfor the second antenna group may be performed through L1/L2 controlsignaling.

Advantageous Effects

According to the embodiments of the present invention, it is possible toefficiently perform channel sounding using a plurality of antennas in awireless communication system.

Advantages of the present invention are not limited to those describedabove and other advantages will be clearly understood by those skilledin the art from the following description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates a network structure of an E-UMTS as an exemplarymobile communication system;

FIG. 2 illustrates structures of a control plane and a user plane of aradio interface protocol between a UE and E-UTRAN based on the 3GPPradio access network standard;

FIG. 3 illustrates physical channels used in a 3GPP system and a generalsignal transmission method using the same;

FIG. 4 illustrates the structure of a radio frame used in an LTE system;

FIG. 5 illustrates the structure of an uplink subframe used in an LTEsystem;

FIG. 6 illustrates a procedure for performing channel sounding in thecase where closed-loop antenna selection is applied in an LTE system;

FIG. 7 illustrates a method for multiplexing Sounding Reference Signals(SRSs) in a Code Division Multiplexing (CDM) manner according to anembodiment of the present invention;

FIG. 8 illustrates a method for multiplexing SRSs in a FrequencyDivision Multiplexing (FDM) manner according to an embodiment of thepresent invention;

FIG. 9 illustrates SRSs in a CDM/FDM manner according to an embodimentof the present invention;

FIGS. 10 to 13 illustrate an example in which SRS resources areallocated in a disjoint manner for each antenna according to anembodiment of the present invention;

FIGS. 14 and 15 illustrate an example in which a plurality of SRStransmission symbols is configured in a subframe according to anembodiment of the present invention;

FIG. 16 illustrates a procedure for performing channel soundingaccording to an embodiment of the present invention; and

FIG. 17 is a block diagram illustrating a Base Station (BS) and a UserEquipment (UE) according to an embodiment of the present invention.

BEST MODE

The above and other configurations, operations, and features of thepresent invention will be easily understood from embodiments of thepresent invention, which are described below with reference to theaccompanying drawings. The embodiments described below are examples inwhich the features of the present invention are applied to a 3GPPsystem.

FIG. 2 is a diagram showing structures of a control plane and a userplane of a radio interface protocol between a UE and E-UTRAN based onthe 3GPP radio access network standard. The control plane refers to apath used for transmitting control messages which are used in the UE andthe network to manage a call. The user plane refers to a path used fortransmitting data generated in an application layer, e.g., voice data orInternet packet data.

A physical (PHY) layer of a first layer provides an information transferservice to an upper layer using a physical channel. The PHY layer isconnected to a Medium Access Control (MAC) layer of an upper layer via atransport channel. Data is transported between the MAC layer and the PHYlayer via the transport channel. Data is also transported between aphysical layer of a transmitting side and a physical layer of areceiving side via a physical channel. The physical channel uses timeand frequency as radio resources. Specifically, the physical channel ismodulated using an Orthogonal Frequency Division Multiple Access (OFDMA)scheme in downlink and is modulated using a Single-Carrier FrequencyDivision Multiple Access (SC-FDMA) scheme in uplink.

A Medium Access Control (MAC) layer of a second layer provides a serviceto a Radio Link Control (RLC) layer of an upper layer via a logicalchannel. The RLC layer of the second layer supports reliable datatransmission. The function of the RLC layer may be implemented by afunctional block within the MAC. A Packet Data Convergence Protocol(PDCP) layer of the second layer performs a header compression functionto reduce unnecessary control information for efficient transmission ofan Internet Protocol (IP) packet such as IPv4 or IPv6 in a radiointerface having a relatively narrow bandwidth.

A Radio Resource Control (RRC) layer located at the bottommost portionof a third layer is defined only in the control plane. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to configuration, re-configuration, and release of radiobearers. The radio bearer refers to a service provided by the secondlayer to transmit data between the UE and the network. To this end, theRRC layer of the UE and the RRC layer of the network exchange RRCmessages. The UE is in an RRC connected mode if an RRC connection hasbeen established between the RRC layer of the radio network and the RRClayer of the UE. Otherwise, the UE is in an RRC idle mode. A Non-AccessStratum (NAS) layer located at an upper level of the RRC layer performsfunctions such as session management and mobility management.

One cell of the eNB is set to use one of bandwidths such as 1.25, 2.5,5, 10, 15, and 20 MHz to provide a downlink or uplink transmissionservice to UEs. Different cells may be set to provide differentbandwidths.

Downlink transport channels for data transmission from the network tothe UE include a Broadcast Channel (BCH) for transmitting systeminformation, a Paging Channel (PCH) for transmitting paging messages,and a downlink Shared Channel (SCH) for transmitting user traffic orcontrol messages. User traffic or control messages of a downlinkmulticast or broadcast service may be transmitted through the downlinkSCH or may be transmitted through an additional downlink MulticastChannel (MCH). Meanwhile, uplink transport channels for datatransmission from the UE to the network include a Random Access Channel(RACH) for transmitting initial control messages and an uplink SCH fortransmitting user traffic or control messages. Logical channels, whichare located at an upper level of the transport channels and are mappedto the transport channels, include a Broadcast Control Channel (BCCH), aPaging Control Channel (PCCH), a Common Control Channel (CCCH), aMulticast Control Channel (MCCH), and a Multicast Traffic Channel(MTCH).

FIG. 3 is a diagram showing physical channels used in a 3GPP system anda general signal transmission method using the same.

A UE performs an initial cell search operation such as establishment ofsynchronization with an eNB when power is turned on or the UE enters anew cell (S301). The UE may receive a Primary Synchronization Channel(P-SCH) and a Secondary Synchronization Channel (S-SCH) from the eNB,establish synchronization with the eNB, and acquire information such asa cell identity (ID). Thereafter, the UE may receive a physicalbroadcast channel from the eNB to acquire broadcast information withinthe cell. Meanwhile, the UE may receive a Downlink Reference Signal (DLRS) in the initial cell search step to confirm a downlink channel state.

Upon completion of the initial cell search, the UE may receive aPhysical Downlink Control Channel (PDCCH) and a Physical Downlink SharedChannel (PDSCH) according to information included in the PDCCH toacquire more detailed system information (S302).

Meanwhile, if the UE initially accesses the eNB or if radio resourcesfor signal transmission are not present, the UE may perform a randomaccess procedure (steps S303 to S306) with respect to the eNB. To thisend, the UE may transmit a specific sequence through a Physical RandomAccess Channel (PRACH) as a preamble (steps S303 and S305), and receivea response message to the preamble through the PDCCH and the PDSCHcorresponding thereto (steps S304 and S306). In the case of acontention-based RACH, a contention resolution procedure may beadditionally performed.

The UE which performs the above procedures may receive a PDCCH/PDSCH(S307) and transmit a Physical Uplink Shared Channel (PUSCH)/PhysicalUplink Control Channel (PUCCH) (S308) according to a generaluplink/downlink signal transmission procedure. Control informationtransmitted by the UE to the eNB through uplink or received by the UEfrom the eNB through downlink includes a downlink/uplinkAcknowledgement/Negative Acknowledgement (ACK/NACK) signal, a ChannelQuality Indicator (CQI), a Precoding Matrix Index (PMI), a RankIndicator (RI), and the like. In the case of the 3GPP LTE system, the UEmay transmit the control information such as CQI/PMI/RI through thePUSCH and/or the PUCCH.

FIG. 4 is a diagram showing the structure of a radio frame used in anLTE system.

Referring to FIG. 4, the radio frame has a length of 10 ms (327200T_(s)) and includes 10 subframes each having the same size. Each of thesubframes has a length of 1 ms and includes two slots. Each of the slotshas a length of 0.5 ms (15360 T_(a)). In this case, T_(s) denotes asampling time, and is represented by T_(s)=I/(15 kHz×2048)=3.2552×10⁻⁸(about 33 ns). Each slot includes a plurality of OFDM symbols in a timedomain and includes a plurality of Resource Blocks (RBs) in a frequencydomain. In the LTE system, one RB includes 12 subcarriers×7 (or 6) OFDMsymbols. A Transmission Time Interval (TTI) which is a unit time fordata transmission may be determined in units of one or more subframes.The above-described structure of the radio frame is purely exemplary andvarious modifications may be made in the number of subframes included ina radio frame, the number of slots included in a subframe, or the numberof OFDM symbols included in a slot.

FIG. 5 is a diagram illustrating the structure of an uplink subframeused in an LTE system.

As shown in FIG. 5, a 1 ms subframe 500, which is a basic unit of uplinktransmission of LTE, includes two 0.5 ms slots 501. Assuming that it hasa normal Cyclic Prefix (CP) length, each slot includes 7 symbols 502 andone symbol corresponds to one SC-FDMA symbol. A resource block 503 is aresource allocation unit which corresponds to 12 subcarriers in thefrequency domain and corresponds to one slot in the time domain. Astructure of an uplink subframe of LTE is mainly divided into a dataarea 504 and a control area 505. Here, the data area is a series ofcommunication resources that are used to transmit data such as audio ora packet to each UE and corresponds resources other than the controlarea in the subframe. The control area is a series of communicationresources that are used to transmit a downlink channel quality report,an ACK/NACK to a downlink signal, an uplink scheduling request, or thelike from each UE.

As shown in the example of FIG. 5, a Sounding Reference Signal (SRS) istransmitted in an interval within a subframe in which the last SC-FDMAsymbol in the subframe is located in the time domain and is transmittedthrough a data transmission band in the frequency domain. SRSs of anumber of UEs that are transmitted through the last SC-FDMA symbol ofthe same subframe can be discriminated from each other according to thefrequency location/sequence. SRS generation, physical resource mapping,multiplexing methods, resource allocation, and the like are describedbelow in detail with reference to the 3GPP LTE (Release 8).

An SRS is constructed of a Constant Amplitude Zero Auto Correlation(CAZAC) sequence. SRSs transmitted from a number of UEs are CAZACsequences (r^(SRS)(n)=r_(u,v) ^((α))(n)) having different cyclic shiftvalues (α) according to the following Expression 1.

$\begin{matrix}{\alpha = {2\pi \; \frac{n_{SRS}^{cs}}{8}}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, n_(SRS) ^(es) is a value set for each UE by the higher layer andhas an integer value between 0 and 7.

Each CAZAC sequence generated from one CAZAC sequence through cyclicshifting has a zero correlation with other CAZAC sequences having cyclicshift values different from its cyclic shift value. Using thesecharacteristics, SRSs of the same frequency region can be discriminatedaccording to the sequence CAZAC sequence cyclic shift values. An SRS ofeach UE is allocated to a frequency according to a parameter that is setby the eNode B. The UE performs frequency hopping of the SRS to allowthe SRS to be transmitted over the overall uplink data transferbandwidth.

A detailed method for mapping physical resources for transmitting an SRSin an LTE system is described below.

First, each SRS sequence r^(SRS)(n) is multiplied by β_(SRS) in order tosatisfy transmission power P^(SRS) and then the SRS sequences, startingfrom an SRS sequence r^(SRS)(0), are sequentially mapped to ResourceElements (REs) whose index is (k, l) according to the followingExpression 2.

$\begin{matrix}{a_{{{2k} + k_{0}},l} = \left\{ \begin{matrix}{\beta_{SRS}{r^{SRS}(k)}} & {{k = {0,1,\mspace{14mu} \ldots}}\;,{M_{{sc},b}^{RS} - 1}} \\0 & {otherwise}\end{matrix} \right.} & \left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, k₀ indicates a frequency region start point of the SRS andM_(sc,b) ^(RS) is the length (i.e., bandwidth) of an SRS sequencerepresented in units of subcarriers as defined in the followingExpression 3.

M _(sc,b) ^(RS) =m _(SRS,b) N _(sc) ^(RB)/2  [Expression 3]

In Expression 3, m_(SRS,b) is a value signaled from an eNode B accordingto an uplink bandwidth N_(RB) ^(UL) as shown in the following Tables 1to 4.

A cell specific parameter C_(SRS) which is an integer value between 0and 7 and a UE specific parameter B_(SRS) which is an integer valuebetween 0 and 3 are required to acquire m_(SRS,b). The values of C_(SRS)and B_(SRS) are given by the higher layer.

TABLE 1 b^(hop) = 0, 1, 2, 3, values for the uplink bandwidth of 6 ≦N_(RB) ^(UL) ≦ 40. SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth BandwidthBandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2B_(SRS) = 3 C_(SRS) m_(SRS, b) N_(b) m_(SRS, b) N_(b) m_(SRS, b) N_(b)m_(SRS, b) N_(b) 0 36 1 12 3 4 3 4 1 1 32 1 16 2 8 2 4 2 2 24 1 4 6 4 14 1 3 20 1 4 5 4 1 4 1 4 16 1 4 4 4 1 4 1 5 12 1 4 3 4 1 4 1 6 8 1 4 2 41 4 1 7 4 1 4 1 4 1 4 1

TABLE 2 b_(hop) = 0, 1, 2, 3, values for the uplink bandwidth of 40 <N_(RB) ^(UL) ≦ 60. SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth BandwidthBandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2B_(SRS) = 3 C_(SRS) m_(SRS, 0) N₀ m_(SRS, 1) N₁ m_(SRS, 2) N₂ m_(SRS, 3)N₃ 0 48 1 24 2 12 2 4 3 1 48 1 16 3 8 2 4 2 2 40 1 20 2 4 5 4 1 3 36 112 3 4 3 4 1 4 32 1 16 2 8 2 4 2 5 24 1 4 6 4 1 4 1 6 20 1 4 5 4 1 4 1 716 1 4 4 4 1 4 1

TABLE 3 b_(hop) = 0, 1, 2, 3, values for the uplink bandwidth of 60 <N_(RB) ^(UL) ≦ 80. SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth BandwidthBandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2B_(SRS) = 3 C_(SRS) m_(SRS, 0) N₀ m_(SRS, 1) N₁ m_(SRS, 2) N₂ m_(SRS, 3)N₃ 0 72 1 24 3 12 2 4 3 1 64 1 32 2 16 2 4 4 2 60 1 20 3 4 5 4 1 3 48 124 2 12 2 4 3 4 48 1 16 3 8 2 4 2 5 40 1 20 2 4 5 4 1 6 36 1 12 3 4 3 41 7 32 1 16 2 8 2 4 2

TABLE 4 b_(hop) = 0, 1, 2, 3, values for the uplink bandwidth of 80 <N_(RB) ^(UL) ≦ 110. SRS SRS- SRS- SRS- SRS- bandwidth BandwidthBandwidth Bandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1B_(SRS) = 2 B_(SRS) = 3 C_(SRS) m_(SRS, 0) N₀ m_(SRS, 1) N₁ m_(SRS, 2)N₂ m_(SRS, 3) N₃ 0 96 1 48 2 24 2 4 6 1 96 1 32 3 16 2 4 4 2 80 1 40 220 2 4 5 3 72 1 24 3 12 2 4 3 4 64 1 32 2 16 2 4 4 5 60 1 20 3 4 5 4 1 648 1 24 2 12 2 4 3 7 48 1 16 3 8 2 4 2

As described above, the UE may perform frequency hopping of the SRS toallow the SRS to be transmitted over the overall uplink data transferbandwidth. This frequency hopping is set by a parameter b_(hop) having avalue of 0 to 3 that is given by the higher layer.

When the frequency hopping of the SRS is disabled (i.e., whenb_(hop)≧B_(SRS)), the frequency position index n_(b) has a specificvalue as shown in the following Expression 4. In Expression 4, n_(RRC)is a parameter given by the higher layer.

n _(b)=└4n _(RRc) /m _(SRS,b)┘mod N _(b)  [Expression 4]

On the other hand, when the frequency hopping of the SRS is enabled(i.e., when b_(hop)>B_(SRS)), the frequency position index n_(b) isdefined according to the following Expressions 5 and 6. In Expression 4,n_(RRC) is a parameter given by the higher layer.

$\begin{matrix}{n_{b} = \left\{ \begin{matrix}{\left\lfloor {4n_{RRC}\text{/}m_{{SRS},b}} \right\rfloor {mod}\mspace{14mu} N_{b}} & {b \leq b_{hop}} \\{\left\{ {{F_{b}\left( n_{SRS} \right)} + \left\lfloor {4n_{RRC}\text{/}m_{{SRS},b}} \right\rfloor} \right\} {mod}\mspace{14mu} N_{b}} & {otherwise}\end{matrix} \right.} & \left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack \\{{F_{b}\left( n_{SRS} \right)} = \left\{ \begin{matrix}{{\left( {N_{b}\text{/}2} \right)\left\lfloor \frac{n_{SRS}\mspace{11mu} {mod}\mspace{14mu} {\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}}}{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}} \right\rfloor} + \left\lfloor \frac{n_{SRS}\mspace{11mu} {mod}\mspace{11mu} {\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}}}{2{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}}} \right\rfloor} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {even}} \\{\left\lfloor {N_{b}\text{/}2} \right\rfloor \left\lfloor {n_{SRS}\text{/}{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}}} \right\rfloor} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {odd}}\end{matrix} \right.} & \left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Here, n_(SRS) is a parameter for calculating the number of times an SRShas been transmitted as is defined in the following Expression 7.

$\begin{matrix}{n_{SRS} = \left\{ \begin{matrix}{{{2N_{SP}n_{f}} + {2\left( {N_{SP} - 1} \right)\left\lfloor \frac{n_{s}}{10} \right\rfloor} + \left\lfloor \frac{T_{offset}}{T_{offset\_ max}} \right\rfloor},} \\{\left\lfloor {\left( {{n_{f} \times 10} + \left\lfloor {n_{s}\text{/}2} \right\rfloor} \right)\text{/}T_{SRS}} \right\rfloor,}\end{matrix} \right.} & \left\lbrack {{Expression}\mspace{14mu} 7} \right\rbrack\end{matrix}$

for 2 ms SRS periodicity of TDD frame structure otherwise

Here, T_(SRS) denotes a period of the SRS and T_(offset) denotes asubframe offset of the SRS. In addition, n_(s) denotes a slot number andn_(f) denotes a frame number.

UE specific SRS setting indices I_(SRS) for setting the period T_(SRS)and the subframe offset T_(offset) of the SRS are shown in the followingTables 5 and 6 respectively for FDD and TDD.

TABLE 5 UE Specific SRS Periodicity T_(SRS) and Subframe OffsetConfiguration T_(offset), FDD. SRS Configuration SRS Periodicity SRSSubframe Index I_(SRS) T_(SRS) (ms) Offset T_(offset) 0-1 2 I_(SRS) 2-65 I_(SRS) − 2   7-16 10 I_(SRS) − 7  17-36 20 I_(SRS) − 17 37-76 40I_(SRS) − 37  77-156 80 I_(SRS) − 77 157-316 160  I_(SRS) − 157 317-636320  I_(SRS) − 317  637-1023 reserved reserved

TABLE 6 UE Specific SRS Periodicity T_(SRS) and Subframe OffsetConfiguration T_(offset), TDD. Configuration SRS Periodicity SRSSubframe Index I_(SRS) T_(SRS) (ms) Offset T_(offset) 0 2 0, 1 1 2 0, 22 2 1, 2 3 2 0, 3 4 2 1, 3 5 2 0, 4 6 2 1, 4 7 2 2, 3 8 2 2, 4 9 2 3, 410-14 5 I_(SRS) − 10 15-24 10 I_(SRS) − 15 25-44 20 I_(SRS) − 25 45-8440 I_(SRS) − 45  85-164 80 I_(SRS) − 85 165-324 160  I_(SRS) − 165325-644 320  I_(SRS) − 325  645-1023 reserved reserved

TABLE 7 k_(SRS), TDD subframe index n 1 6 1st symbol 2nd symbol 1stsymbol 2nd symbol 0 of UpPTS of UpPTS 2 3 4 5 of UpPTS of UpPTS 7 8 9k_(SRS) in case 0 1 2 3 4 5 6 7 8 9 UpPTS length of 2 symbols k_(SRS) incase 1 2 3 4 6 7 8 9 UpPTS length of 1 symbol

FIG. 6 illustrates a method for transmitting an SRS for each antennawhen antenna selection is applied in an LTE system. In a conventionalLTE system, a UE applies an open-loop antenna selection or closed-loopantenna selection scheme to switch single power amplifier output orsingle antenna transmission based on single RF power amplifier chain fora plurality of physical antennas (for example, 2 physical antennas) inthe time resource region when performing uplink transmission.

Specifically, FIG. 6 illustrates an example in which an SRS istransmitted using a closed-loop selection transmission method. Morespecifically, FIG. 6 illustrates an example in which a frequencyresource region is allocated to an SRS for each antenna at the timing ofSRS transmission in the case where an SRS band smaller than the entiresystem band is applied and SRS hopping is applied. In the case where SRShopping is not applied, an SRS is transmitted alternately using eachindividual antenna at the position of transmission and the same SRS bandfor each individual SRS transmission time. Unlike this method, an uplinktransmission entity (i.e., a UE or a relay node) such as an LTE-A UE canperform uplink transmission to a plurality of antennas while having aplurality of transmission antennas and a plurality of RF power amplifierchains. If it is assumed in this situation that the method oftransmitting an SRS for each individual antenna described above isapplied as an SRS transmission method, there is a problem in that it isnecessary to turn off a power amplifier of an antenna which does nottransmit an SRS in one or more SRS transmission symbols (for example,OFDM symbols or SC-FDMA symbols) in a subframe in an LTE-A system towhich a simultaneously transmission scheme which uses a plurality of RFpower amplifier chains and a plurality of antennas is applied. Inaddition, there may also be a problem in that the transmission power ofan antenna for transmitting an SRS is limited to 1/(the number oftransmission antennas) relative to single antenna transmission power. Inthe case of LTE, an arbitrary UE uses, for SRS transmission, the lastsymbol of a subframe at the time of SRS transmission. In the LTE-Asystem, a plurality of symbols may be used for SRS transmission and thepositions of the symbols in a subframe may be different from those inthe case of the LTE system although the same number and/or positions ofSRS transmission symbols as those of the LTE system may also be appliedto the LTE-A system. In addition, a method of configuring SRStransmission and other uplink channel transmission in an LTE-A uplinktransmission scheme which allows non-contiguous RB transmission andcorresponding PUSCH/PUCCH and PUCCH/PUCCH decoupling (or simultaneoustransmission of different channels) may also be applied in a differentmanner from that of the LTE system. In consideration of these facts, amethod of transmitting an SRS of each individual antenna, which isdifferent from the conventional SRS transmission method, may be definedin the LTE-A system.

The present invention suggests a method of transmitting an SRS for thepurpose of channel sounding for performing status information relatedmeasurement of channel(s) configured for uplink transmission in asituation in which an uplink transmission entity (i.e., a UE or a relaynode) in the LTE-A system can perform uplink transmission to a pluralityof antennas while having a plurality of transmission antennas and aplurality of RF power amplifier chains. Suggestions of the presentinvention can be applied to any mobile communication system in whichuplink transmission is simultaneously performed through each individualantenna through a plurality of RF power/signal amplifiers and aplurality of transmission antennas although the present invention hasbeen described with reference to an LTE-A system throughout thisspecification.

Embodiment 1 Method of Multiplexing Individual SRSs that are Generatedin Units of Transmission Antennas (when Precoding is not Applied to SRS)or in Units of Transmission Layers (when Precoding is Applied to SRS) ina Multi-Antenna Situation

{Technology Associated with Allocation of Parts Associated with SRSResource Allocation in LTE}

The following is a summary of information items that are associated withSRS transmission resource allocation to an arbitrary UE in theconventional technology described above.

Transmission Comb k_(TC)

k_(TC) is a parameter used to derive a frequency region start point ofan SRS. One of 0 and 1 is used as an offset value associated with“transmission comb”. This parameter is defined as a UE-specific RRCparameter and is indicated through UE-specific RRC signaling. Thedefinition of k_(TC) is described in section 5.5.3.2 of the 3GPPTechnical Specification (TS) 36.211.

Starting Physical Resource Block Allocation n_(RRC)

n_(RRC) is a UE-specific RRC parameter indicating the frequency domainposition of an SRS and is indicated through UE-specific RRC signaling.The definition of n_(RRC) is described in section 5.5.3.2 of the 3GPP TS36.211.

SRS Transmission Duration: Single or Indefinite (Until Impossible)

This information is defined as a UE-specific RRC parameter and istransmitted through UE-specific RRS signaling. In the case where thisparameter is set to “single”, an SRS is transmitted only once and, inthe case where this parameter is set to “indefinite”, an SRS continuesto be transmitted according to the set configuration unless in a SRStransmission disabled situation or unless corresponding signaling isreceived.

SRS Configuration Index I_(SRS) for SRS Periodicity and SRS SubframeOffset T_(offset)

These information items are defined as UE-specific RRC parameters andare transmitted through UE-specific RRC signaling. Specifically, theseparameters are information indicating the transmission period of an SRSand an arbitrary subframe offset. These information items are configuredfor TDD as shown in Table 5 and are configured for FDD as shown in Table6. These parameters are described in section 8.2 of the 3GPP TS 36.211.

SRS Bandwidth B_(SRS)

This information is defined as a UE-specific RRC parameter and istransmitted through UE-specific RRS signaling. As index information usedto define an SRS bandwidth, this parameter is specified as one of 0, 1,2, and 3. This parameter is used for physical resource mapping asdescribed in section 5.5.3.2 of the 3GPP Technical Specification (TS)36.211 in the conventional technology described above.

Frequency Hopping Bandwidth b_(hop)

This information is defined as a UE-specific RRC parameter and istransmitted through UE-specific RRS signaling. As index information usedto configure frequency hopping of an SRS, this parameter is specified asone of 0, 1, 2, and 3. This parameter is used for physical resourcemapping as described in section 5.5.3.2 of the 3GPP TechnicalSpecification (TS) 36.211 in the conventional technology describedabove.

Cyclic Shift n_(SRS) ^(es)

This parameter is defined as a UE-specific RRC parameter and istransmitted through UE-specific RRS signaling. As index information ofcyclic shift of a sequence used to generate an SRS sequence, this cyclicshift parameter is used as orthogonal resources in code multiplexing ofSRSs for a number of UEs. This parameter is used to generate an SRS codesequence as described in section 5.5.3.2 of the 3GPP TechnicalSpecification (TS) 36.211 in the conventional technology describedabove.

Base Sequence Index

This information characterizes an SRS sequence together with the cyclicshift when generating an SRS sequence. This information is derived froma base sequence index of a PUCCH.

In the LTE system, physical resource mapping and resource allocation forSRSs of individual UEs are performed based on the parameters describedabove. The most important thing, which should be taken intoconsideration when designing physical resource mapping and resourceallocation for uplink SRS transmission in the LTE-A system, is that theLTE-A UE performs uplink transmission using a plurality of transmissionantennas at an arbitrary time using RF chains and a plurality of poweramplifiers while the LTE UE performs uplink transmission through asingle transmission antenna at an arbitrary time using a single poweramplifier. The following are a summary of important designconsiderations in main suggestions of the present invention, focusingupon this fact.

-   -   Compared to a conventional LTE UE, an arbitrary LTE-A UE is        likely to increase the frequency of attempts to perform SRS        transmission for channel sounding for all (physical) antennas of        the UE over a full system band. Therefore, delay may occur in        association with full band channel sounding for all uplink        (physical) antennas and a different delay condition may be        applied when SRS transmission of each layer or each individual        antenna is applied. This may impose limitation to acquisition of        optimal throughput gain when Doppler frequencies are present in        association with channel-dependent scheduling of an eNode B.    -   In the case where the LTE-A inherits an LTE scheme in which SRS        transmission symbols are defined according to a TDM scheme in        which an SRS is transmitted in a partial time region of an        arbitrary subframe for the purpose of channel sounding, symbols        carrying a PUSCH or a PUCCH and a symbol(s) carrying an SRS may        be discriminated from each other in a subframe. In this        situation, an SRS may be transmitted using a different number of        antennas from the number of transmission antennas through which        a PUSCH or a PUCCH is transmitted. In this case, a power pooling        situation in which power of a series of transmission antennas        which are turned off is distributed to a transmission antenna(s)        that is turned on may occur when it is possible to turn some        transmission antennas on or off at boundaries between        PUSCH/PUCCH transmission symbols and SRS transmission symbols.        It takes time to perform such on/off switching of power and/or        signal amplifiers. To cope with this situation, it is possible        to define a series of guard times using a series of time sample        regions at the last time sample interval of symbols prior to        symbol (e.g., OFDM or SC-FDMA symbol) boundaries between an SRS        transmission symbol(s) and PUSCH or PUCCH transmission symbols        in a subframe (or in a symbol interval) or to define a series of        guard times using a series of time sample regions at start        portions of symbols after the boundaries depending on the        importance of the symbols. In the latter case, there may be no        need to define a separate guard time if a time sample region of        the guard time is defined in a cyclic shift region. However,        this scheme may cause overall throughput degradation. Therefore,        as a different scheme, it is possible to consider an SRS        reception multiplexing allocation scheme in which the number of        transmission antennas used for SRS transmission on an arbitrary        LTE-A UE is set to be as equal to the number of transmission        antennas used for PUSCH or PUCCH transmission in a different        symbol interval as possible without defining such guard times.        This can be taken into account as one important consideration in        some suggestions of SRS transmission resource allocation or        multiplexing schemes according to the present invention.    -   One of the important considerations when a receiver of an eNode        B/cell performs uplink channel measurement using an SRS in the        case where a UE transmits an SRS with suggested (or limited) UE        transmission power is a transmission Power Spectral Density        (PSD) level in a frequency region for an SRS transmission        signal. Settings associated with allocation of power for        individual SRS transmission while taking into consideration        output power of an arbitrary symbol when performing SRS        transmission resource allocation include setting of an SRS        transmission band and setting of the degree of multiplexing in        which Code Division Multiplexing (CDM) and/or Frequency Division        Multiplexing (FDM) is implemented in an arbitrary frequency        resource region. In addition, another consideration that needs        to be made on an LTE-A UE is the number of uplink transmission        antennas that are simultaneously used. That is, as the total        number of SRS transmissions required in a cell increases as an        extended SRS transmission procedure is required compared to the        conventional SRS transmission in a situation in which an LTE-A        UE supports transmission through multiple antennas at an        arbitrary transmission time, there is a need to provide methods        for providing a coverage in association with SRSs similar to the        coverage of the LTE system and multiplexing and power allocation        methods for supporting reliable measurement of individual SRS        transmission. Another important consideration that should be        taken into account is whether or not an LTE-A UE can perform        antenna power pooling when performing multiple antenna        transmission as described above.

The present invention suggests basic SRS multiplexing and resourceallocation methods for supporting the important considerations in SRSdesign of the LTE-A described above.

Embodiment 1 Physical Resource Multiplexing for an SRS in an SRSTransmission Subframe

In the case where another series of PUSCHs or PUCCHs is transmitted in asubframe including an SRS transmission symbol in an LTE-A system thatsupports multiple antenna transmission based on the configuration of RFchains and multiple power amplifiers, SRS transmission associated withlayers (or streams) or physical or logical antennas (or antenna ports)that are used for PUSCHs or PUCCHs is performed through SRS transmissionsymbol(s) allocated to a subframe such as the channels (i.e., the PUSCHsor PUCCHs). As an SRS multiplexing method for supporting this SRStransmission, it is possible to consider CDM, FDM, or CDM/FDM in an SRStransmission symbol in an arbitrary subframe.

A factor for determining the basic multiplexing capacity in CDM is thenumber of available cyclic shifts in an SRS sequence. The number ofavailable cyclic shifts may be determined based on a relation betweenthe length of a Cyclic Prefix (CP) interval of a transport symbol (forexample, an OFDM symbol or an SC-FDMA symbol) and a delay spread valueof the channel. In one example, the number of available cyclic shiftsmay be explicitly configured as an RRC parameter in a higher layer(i.e., the RRC layer) for all or part of the cyclic shifts that arerequired for SRS transmission in an arbitrary LTE-A UE and then may besignaled through UE-specific RRC signaling. For some cyclic shifts, thenumber of available cyclic shifts may be implicitly configured withoutexplicit signaling. As circumstances require, a base sequence index,which is referred to as a root index, in an SRS sequence may also be afactor for determining the multiplexing capacity together with thecyclic shift. This scheme may be selectively applied depending on thetransmission mode of the UE or the channel environment. The indicationof the scheme may be implicitly or indirectly set through a series ofother signaling information. It is also possible to define an explicitsignaling parameter for indicating the scheme.

FIG. 7 illustrates exemplary CDM for the case where an SRS transmissionsymbol is the last of the transmission symbols of a subframe in which anarbitrary LTE-A UE transmits an SRS. Although FIG. 7 illustrates asituation in which SRSs of an LTE-A UE which are multiplexed in a CDMmanner are transmitted with a limited SRS transmission band, the SRStransmission band may have a various size including the full systemband.

As a specific example, it is preferable that CDM be applied toenvironments associated with UL coordinated multiple point (CoMP)transmission and reception and UL/DL CoMP and associated with LTE-A UEsrather than power-limited environments from the viewpoint of UEtransmission power through power control due to high geometry.Indication of cyclic shifts of the degree of application of codedivision (and indication of base sequence indices associated with thetotal or partial number of cyclic shifts requiring the base sequenceindices) may be additionally defined explicitly as an SRS related RRCparameter in association with application of CDM or CDM/FDM for SRSsthat are to be transmitted by an arbitrary UE that performs multipleantenna transmission using multiple power amplifiers and/or RF chains.Here, examples of the degree of application of code division include avalue associated with the number of code resource units to be used fortransmission. In addition, the number of code resources that are usedaccording to a UE MIMO transmission mode may be defined as a presetvalue. Alternatively, the number of code resources may be defined as anexplicit RRC parameter and cyclic shift indices of the individual coderesources (or base sequence indices in addition to the cyclic shiftindices) and the remaining values may be implicitly specified using arule or a series of offsets using one explicitly specified value.

As one factor for determining the degree of multiplexing in an arbitrarySRS transmission symbol when applying the FDM scheme, it is possible toconsider an interval between each subcarrier used for transmission in anarbitrary frequency region, i.e., both a discrete comb mapping ratio(which can also be referred to as a comb division ratio) and a unit SRStransmission band allocated to an arbitrary UE. For example, in the LTE,the discrete comb mapping ratio is set to 2 so as to be used fordiscriminating resources between full-band soundings and sub-bandsoundings or for discriminating resource allocation between evensubcarrier indices and odd subcarrier indices. The SRS transmission bandhas also been defined as respective values of various cases for eachsystem band in a table. In the LTE-A, it is also possible to apply anincreased discrete comb mapping ratio compared to the LTE when takinginto consideration the multiple antenna transmission environment. Forexample, as 2*(the number of transmission antennas) or 2*(the number oftransmission layers), the comb division ratio may have a value of 2 or 4in the case of 2Tx and may have a value of 2, 4, 6, or 8 in the case of4Tx. In the case where the comb division ratio is increased in thismanner or is 2, all or partial comb frequency offsets may be usedmultiplexing of an SRS sequence of each antenna. In association with theSRS transmission band, power of each antenna of an arbitrary UE thatsupports multiple antenna transmission may be reduced by an amountcorresponding to the number of the antennas compared to the singleantenna or antenna selection case. Therefore, in order to secure thecoverage of SRS transmission of each individual antenna (or individuallayer) or to support reliable measurement of the same, it is possible toadditionally define a smaller SRS transmission band in an arbitrarysystem band than to the case of an LTE UE that performs single antennatransmission. That is, it is possible to define smaller SRS transmissionbands in an arbitrary system band than the case where SRS transmissionof the conventional LTE is possible and to add candidates for the SRStransmission band with higher granularity than the same case. As ascheme that can be applied independent of this scheme or in addition tothis scheme, it is possible to specify candidates to be applied in theform of a subset of the entire set of SRS transmission relatedparameters (including the transmission band) configured through RRCparameters for the case of multiple antenna transmission. The candidatesmay be specified through designation of an uplink transmission mode (forexample, UE-specific RRC signaling or L1/L2 control signaling). It isalso possible to define and signal an additional RRC parameter. Throughthese schemes, it is possible to maintain a subcarrier power spectraldensity (PSD) level that is required from the viewpoint of measurementquality or the coverage in association with SRS transmission for eachantenna or layer. One method, which can be applied in parallel with orindependent of this scheme, increases the discrete comb mapping ratiofor UEs, each having a plurality of transmission antennas or for all UEsin a cell (eNode B). In this method, it is possible to relativelyincrease the power spectral density (PSD) of physical resources (i.e.,subcarriers or resource elements (REs)) by reducing, in the frequencydomain, the density of physical resources to which power allocated to anarbitrary antenna is allocated in a given SRS transmission band. Inaddition, it is possible to implement a series of FDM multiplexing bymapping SRS sequences transmitted through different (physical)transmission antennas to comb frequency offsets (i.e., unit combpatterns) that are obtained through the increase of the discrete combmapping ratio. Channel measurement performance may be reduced as thediscrete comb mapping ratio increases. In order to prevent the reductionof channel measurement performance, the discrete comb mapping ratio maybe set to 3 in a situation in which the number of UE (physical)transmission antennas is 2 or 4. In this case, one comb pattern may beallocated for a specified range of all or wider channel soundings and,in the case where the number of transmission antennas is 2, respectiveSRS sequences of the antennas may be differently mapped to 2 remainingcomb patterns. On the other hand, in the case where the number of UEtransmission antennas is 4, the transmission antennas may be grouped to2 antenna groups, each including 2 antennas, and the 2 antenna groupsmay be differently mapped to the 2 remaining comb patterns. In addition,it is possible to achieve multiplexing by allocating different frequencybands or code resources (i.e., cyclic shifts) to 2 transmission antennasin the antenna group.

FIG. 8 illustrates exemplary FDM for the case where an SRS transmissionsymbol is the last of the transmission symbols of a subframe in which anarbitrary LTE-A UE transmits an SRS. Although FIG. 8 illustrates asituation in which SRSs of an LTE-A UE which are multiplexed in a FDMmanner are transmitted with a limited SRS transmission band, the SRStransmission band may have a various size including the full systemband. Here, it is to be noted that representations of SRS transmissionbands, which are shown as bands discriminated from each other, may alsobe applied to the FDM scheme for discrete physical comb patternsdescribed in the present invention.

It is preferable that the FDM or CDM/FDM scheme suggested in the presentinvention be applied to a UE which is in a non-power-limited situation.For example, it is preferable that the SRS FDM or CDM/FDM scheme enablenon-contiguous Resource Block (RB) allocation through clustered DiscreteFourier Transform—spread—Orthogonal Frequency Division Multiple Access(DFT-s-OFDMA) in uplink or that the SRS FDM or CDM/FDM scheme be appliedto a UE that can use component carrier (CC). To accomplish this, in thecase where an indication of the application of the clustered DFT-s-OFDMAis explicitly or implicitly provided from an eNode B or an indication ofthe application of uplink multiple component subcarriers is explicitlyor implicitly provided from an eNode B, it is possible to apply amultiplexing scheme in the form of applying FDM or CDM/FDM whenmultiplexing SRSs based on signaling of the indication. It is possibleto define a parameter indicating that the SRS configuration is to bechanged depending on the uplink transmission mode of the UE or dependingon whether or not power of the UE is limited and to provide theindication through UE-specific RRC signaling or L1/L2 control signaling.

When the CDM/FDM scheme is applied, there is a need to take intoconsideration correlations between parameters for determiningmultiplexing granularity and capacity of CDM and parameters fordetermining multiplexing granularity and capacity of FDM rather than totake into consideration a simple combination of the two multiplexingschemes. For example, setting of the discrete comb mapping ratio fordetermining the frequency component density and the multiplexing levelof an SRS signal in the FDM scheme has an influence upon determining thenumber of available cyclic shifts associated with the CDM capacity.Specifically, increasing the discrete comb mapping ratio value has aneffect of decreasing the number of available cyclic shifts in the caseof CDM. In addition, in the case where the base sequence index is set asa code resource region of CDM, the size of available base sequence indexpools is determined in proportion to the size of an SRS transmissionband of FDM. In the case where CDM/FDM is applied for SRS transmissionmultiplexing of LTE-A UEs that supports multiple antenna transmissionusing multiple power amplifiers and/or RF chains taking intoconsideration this fact, it is possible to define detailed schemes ofCDM/FDM not only basically based on the efficiency of channel soundingbut also based on factors such as signaling overhead reduction andbackward compatibility. For example, in the case where PUSCH or PUCCHmultiplexing is taken into consideration while achieving a designminimizing additional indication overhead of used cyclic shifts ordecreasing the capacity of cyclic shifts, it is possible to configureSRS resource allocation/multiplexing as shown in FIG. 9 under theassumption that all SRSs are transmitted within an SRS transmissionsymbol according to the MIMO transmission mode or according to antennasconfigured for the UE.

FIG. 9 illustrates an example of CDM/FDM in an uplink subframe of a UE(for example, an LTE-A UE) that transmits an SRS. Although FIG. 9illustrates a situation in which SRSs of an LTE-A UE which aremultiplexed in a CDM/FDM manner are transmitted with a limited SRStransmission band, the SRS transmission band may have a various sizeincluding the full system band. The following is a more detaileddescription of the example of FIG. 9. When an arbitrary LTE-A UE has MSRSs (M>0) that are to be transmitted in an arbitrary subframe, it ispossible to use, as a method of allocating M SRS resources for SRStransmission, a method of allocating the number of cyclic shifts andindices to be used respectively for N used SRS transmission bands inorder to optimize resource utilization. Unlike this method, it ispossible to use a method in which the number and index information of Pavailable cyclic shift resources (optionally together with a basesequence as a resource allocation element) and the number and positionindex information of N SRS transmission bands as illustrated in FIG. 9in order to simplify signaling overhead or configuration. Here, it maybe considered that N and P are specified such that N*P is equal to orgreater than M. As a method of allocating respective resources for MSRSs, it is possible to apply a band-first assignment scheme for the SRStransmission band and it is also possible to apply a code-firstassignment scheme for the cyclic shift.

In addition to the CDM, FDM, or CDM/FDM scheme described above, it ispossible to apply, as other candidates, a series of SRS resourcemultiplexing and configurations such as CDM/TDM, FDM/TDM, andCDM/FDM/TDM to arbitrary LTE-A UEs. The following is a description of amethod of changing the configuration of SRS, focusing upon the LTE-A. Inthe case of LTE, when SRS transmission is enabled, an SRS continues tobe transmitted until a transmission termination event occurs (i.e.,until SRS transmission is disabled) and an RRC parameter for releasingSRS transmission has not been defined. However, it can be consideredthat an SRS transmission release parameter is additionally set for anLTE-A UE. It is also possible to set the number of transmissions of anSRS or an SRS transmission time according to period configurationinformation after SRS transmission is enabled through UE-specific RRCsignaling. It can also be considered that SRS transmission configurationinformation is transmitted using L1/L2 control signaling (for example, aPDCCH or MAC messaging). For example, it is possible to trigger SRStransmission through L1/L2 signaling. In this case, in order toefficiently reduce signaling overhead, L1/L2 control signaling carryingSRS transmission configuration information may be event-triggered or mayhave periodic characteristics. It is possible to employ (but not limitedto) an example in which the number of valid transmissions, atransmission period, period configuration information, and the like aresignaled while being included in L1/L2 control information. Here,periodic SRS transmission may be performed every period using acorresponding subframe and may be performed using consecutive Ssubframes, starting from the time of the transmission period. It is alsopossible to employ a periodic SRS transmission method in which a seriesof offsets are defined and an SRS is transmitted at intervalscorresponding to the offsets. The periodic configuration informationincludes a transmission start point, a period, subframe group allocationinformation (in the case of periodic transmission in units of subframegroups), and the like. There is no need to separately define informationregarding the transmission start time when the method complies with ageneral grant-to-uplink timing relation. In the case where SRStransmission is configured through UE-specific RRC signaling, all orpart of the L1/L2 control information defined according to the presentinvention as described above may be defined as an RRC parameter. Inaddition, in the case where SRS transmission is enabled or triggeredthrough L1/L2 control signaling, it is possible to additionally definean SRS transmission release parameter (or message) in L1/L2 controlsignaling.

In the following, as a more detailed scheme of the method formultiplexing physical resources for an SRS in an arbitrary SRStransmission subframe described above in the embodiment 1, the presentinvention suggests a method for applying an FDM scheme between antennasand a CDM scheme between UEs.

Specifically, the present invention suggests an FDM scheme appliedbetween antennas and a CDM scheme applied between UEs which reuse themethod applied to the conventional LTE sounding channel and maintainsbackward compatibility as much as possible.

i) It is possible to consider a method in which the discrete combmapping ratio (or repetition factor (RPF)) described in the embodiment 1is increased in proportion to the number of antennas (or the number oflayers or the number of ranks).

Option 1) RPF=2 used in LTE may be used without change and, in addition,the RPF for multiple antennas in the LTE-A system which takes intoconsideration multiple antennas may be increased in proportion to thenumber of antennas (or the number of layers or the number of ranks). Inthis case, the length (or duration) M_(sc,b) ^(RS) of an SRS sequencemay be defined as in the following Expression 8.

M _(sc,b) ^(RS) =m _(SRS,b) N _(sc) ^(RB)/{2×L}  [Expression 8]

Here, m_(SRS,b) is a value given for each uplink band N_(RB) ^(UL) andis illustrated in Tables 1 to 4. L denotes the number of transmissionantennas (or layers or ranks) for an SRS.

When the Number of Transmission Antennas (or Layers or Ranks) for SRS is4

RPF=2 may be applied to the conventional LTE and RPF=4 may beadditionally defined for 4 transmission antennas (or layers or ranks) inthe case of LTE-A.

In the conventional LTE, the minimum transmission unit of an SRS for asingle antenna is 4 RBs. Accordingly, 6 REs (=4RB*12 subcarriers/(2*4))are allocated to each antenna (or each layer or each rank) in the casewhere distributed FDM is used for orthogonality between antennas and 4transmission antennas (or 4 layers or 4 ranks) used in the LTE-A areused, taking into consideration the minimum RB allocation. Thus, a6-length sequence for an SRS is required in the LTE-A. In this case, aCAZAC sequence (a ZC sequence or a sequence generated based on atruncation or extension scheme), a DFT based sequence, a PN sequence, oranother type of orthogonal sequence may be used as the 6-lengthsequence. As a 6-length sequence, a 6-length computer-generated sequencemay be created and used as it has been suggested and used as an RSsequence for 1RB (12-length) and 2RB (24-length) in the conventionalLTE.

In the case where a new length-6 sequence is not defined and only thesmallest 1RB-long (length-12) sequence among sequences currently used inthe LTE is used, it is possible to consider a method of making adefinition such that sounding band allocation of 8 RBs or more ispossible using a parameter defined for sounding channel allocation inthe LTE for the case where transmission of 4 Tx antennas (or 4 layers or4 ranks) is used. For example, it is possible to consider a method ofmaking a definition such that sounding band allocation of 8 RBs or moreis possible using a 3-bit SRS band configuration (srs-BandwidthConfig,C_(SRS)={0, 1, 2, 3, 4, 5, 6, 7}) that is signaled by a higher layer asa cell-specific parameter and a 2-bit SRS band (srs-BandwidthConfig,B_(SRS)={0, 1, 2, 3}) that is signaled by a higher layer as aUE-specific parameter from among the parameters defined in the LTE.

In addition, it is possible to perform multiplexing for 4 transmissionantennas (or layers or ranks) using an FDM scheme for up to 2transmission antennas (layers or ranks) and using a CDM scheme, whichallocates cyclic shift indices different from the indices 1 and 2, forthe transmission antennas (layers or ranks) 3 and 4.

As another method, it is possible to consider a method in which asounding channel is transmitted in a TDM manner for each 2 transmissionantennas (or layers or ranks) through antenna switching for multiplexingSRSs for the 4 transmission antennas (or layers or ranks). In this case,there may be no need to design a small-length sequence due to anincrease in the number of antennas. In the case where uplinktransmission is performed using 4 power amplifiers and 4 transmissionantennas, it is possible to perform multiplexing of SRSs for 4transmission antennas (or layers or ranks) by enabling power-on/offthrough power control signaling, higher layer signaling, controlsignaling, or the like for power amplifiers of antennas that are notused when applying a 1 or 2 antenna switching scheme.

When the Number of Transmission Antennas (or Layers or Ranks) for SRS is2

RPF=2 may be applied to the conventional LTE and RPF=4 may beadditionally defined for 4 transmission antennas (or layers or ranks) inthe case of LTE-A.

The minimum unit for transmitting an SRS for a single antenna used inthe conventional LTE described in the related art is 4 RBs. Accordingly,12 REs (=4RB*12 subcarriers/(2*2)) are allocated to each antenna (oreach layer or each rank) when distributed FDM is used for orthogonalitybetween antennas in the case where 2 transmission antennas (or layers orranks) used in the LTE-A are used, taking into consideration the minimumRB allocation. In this case, CDM may be performed for UEs, which use thesame band, using a 1-RB computer-generated sequence defined in the LTE.

As another method, it is possible to consider a method in which asounding channel is transmitted in a TDM manner for each transmissionantennas (or layers or ranks) through antenna switching for multiplexingSRSs for 2 transmission antennas (or layers or ranks). In the case whereuplink transmission is performed using a single power amplifier and 2transmission antennas, it is possible to perform multiplexing of SRSsfor 2 transmission antennas (or layers or ranks) by enablingpower-on/off through power control signaling, higher layer signaling,control signaling, or the like for power amplifiers of antennas that arenot used when applying a 1-antenna switching scheme.

Option 2) The same RPF as that of the LTE may be maintained when thenumber of antennas (or layers or ranks) for uplink sounding transmissionused in the LTE-A system is 1 and the RPF for multiple antennas in theLTE-A system may be increased in proportion to the number of antennas(or the number of layers or the number of ranks) when the number ofantennas (or layers or ranks) for uplink sounding transmission used inthe LTE-A system is 2 or more. In this case, the length (or duration)M_(sc,b) ^(RS) of an SRS sequence may be defined as in the followingExpression 9.

M _(sc,b) ^(RS) =m _(SRS,b) N _(sc) ^(RB)/2·{floor(L/4)+1}  [Expression9]

Here, m_(SRS,b) is a value given for each uplink band N_(RB) ^(UL) andis illustrated in Tables 1 to 4. L denotes the number of transmissionantennas (or layers or ranks) for an SRS.

When the Number of Transmission Antennas (or Layers or Ranks) for SRS is4

RPF=2 may be applied to the conventional LTE and RPF=4 may beadditionally defined for 4 transmission antennas (or layers or ranks) inthe case of LTE-A.

The minimum unit for transmitting an SRS for a single antenna used inthe conventional LTE described in the related art is 4 RBs. Accordingly,12 REs (=4RB*12 subcarriers/(2*2)) are allocated to each antenna (oreach layer or each rank) in the case where distributed FDM is used fororthogonality between antennas and 4 transmission antennas (or 4 layersor 4 ranks) used in the LTE-A are used, taking into consideration theminimum RB allocation. In this case, CDM may be performed for UEs, whichuse the same band, using a 1-RB computer-generated sequence defined inthe LTE.

In addition, it is possible to perform multiplexing for 4 transmissionantennas (or layers or ranks) using an FDM scheme for up to 2transmission antennas (layers or ranks) and using a CDM scheme, whichallocates cyclic shift indices different from the indices 1 and 2, forthe transmission antennas (layers or ranks) 3 and 4.

As another method, it is possible to consider a method in which asounding channel is transmitted in a TDM manner for each 2 transmissionantennas (or layers or ranks) through antenna switching for multiplexingSRSs for the 4 transmission antennas (or layers or ranks). In this case,there may be no need to design a small-length sequence due to anincrease in the number of antennas. In the case where uplinktransmission is performed using 4 power amplifiers and 4 transmissionantennas, it is possible to perform multiplexing of SRSs for 4transmission antennas (or layers or ranks) by enabling power-on/offthrough power control signaling, higher layer signaling, controlsignaling, or the like for power amplifiers of antennas that are notused when applying a 1 or 2 antenna switching scheme.

When the Number of Transmission Antennas (or Layers or Ranks) for SRS is2

RPF=2 may be applied to the conventional LTE and RPF=1 may beadditionally defined for 4 transmission antennas (or layers or ranks) inthe case of LTE-A.

The minimum unit for transmitting an SRS for a single antenna used inthe conventional LTE described in the related art is 4 RBs. Accordingly,24 REs (=4RB*12 subcarriers/(2*1)) are allocated to each antenna (oreach layer or each rank) when distributed FDM is used for orthogonalitybetween antennas in the case where 2 transmission antennas (or layers orranks) used in the LTE-A are used, taking into consideration the minimumRB allocation. In this case, CDM may be performed for UEs, which use thesame band, using a 2-RB computer-generated sequence defined in the LTE.

As another method, it is possible to consider a method in which asounding channel is transmitted in a TDM manner for each transmissionantennas (or layers or ranks) through antenna switching for multiplexingSRSs for 2 transmission antennas (or layers or ranks). In the case whereuplink transmission is performed using a single power amplifier and 2transmission antennas, it is possible to perform multiplexing of SRSsfor 2 transmission antennas (or layers or ranks) by enablingpower-on/off through power control signaling, higher layer signaling,control signaling, or the like for power amplifiers of antennas that arenot used when applying a 1-antenna switching scheme.

The following is a more detailed description of additional aspects ofthe FDM scheme applied between antennas as a method for maintainingbackward compatibility of the SRS transmission scheme as much aspossible.

It is possible to consider a method in which an SRS is transmittedthrough each antenna while maintaining a band allocated to each antennain a disjoint manner by uniformly distributing the full system band suchthat a band allocated for each transmission is proportional to thenumber of antennas to be used for the transmission.

Power-Limited Case

In the power-limited case, there is a need to perform transmission so asto maintain a low Cubic Metric (CM) for an SRS transmitted through eachantenna. Accordingly, it is possible to use a method of performingtransmission in a disjoint manner between antennas. FIGS. 10 and 11illustrate a case of 2 transmission antennas (or layers or ranks) andFIGS. 12 and 13 illustrate a case of 4 transmission antennas. Referringto FIGS. 10 to 13, SRS bands for different antennas are allocated in adisjoint manner such that SRS bands of the antennas are at intervals ofa spacing corresponding to the system band/(the number of transmissionantennas (or layers or ranks)).

Non-power-limited Case (e.g., when clustered DFTs-OFDM, multiplecomponent carriers, or UL ComP is used)

In the non-power-limited situation, there is no need to keep thelimitation of having to maintain the same CM as a single carrier.Accordingly, it is possible to transmit an SRS through differentsounding bands in one symbol. In this case, it is possible to reducetime resources required to sound the entire uplink system band.

Unlike the LTE, the LTE-A supports non-contiguous allocation using anuplink transmission scheme which is based on clustered DFTs-OFDM. In thecase of a sounding channel, non-power-limited UEs can transmit asounding channel using the clustered DFTs-OFDM scheme. Accordingly, itis possible to allocate multiple resources to each antenna. However,assuming that the number of frequency start indices for SRS allocationused in the LTE is maintained at 1 for backward compatibility, it ispossible to use a method in which multiple SRSs are transmitted througheach antenna while maintaining a band allocated to each antenna in adisjoint manner by applying an RPF equal to the number of antennas (orlayers or ranks) between each antenna and uniformly distributing thefull system band such that a band allocated for each transmission isproportional to the number of antennas to be used for the transmission.It is also possible to use a method in which multiple resources, theamount of which depends on the number of clusters, are allocated for SRStransmission.

The methods of option 1) and option 2) of this embodiment describedabove may be applied to the method of applying an RPF between eachantenna.

It is preferable that allocation be performed such that the CM value fora sequence allocated to an SRS that is transmitted using multipleresources through each antenna is not significantly increased comparedto the single carrier CM of the LTE. That is, the CM value oftransmission of an SRS through multiple resources is significantlyincreased in the case where the same cyclic shift as the same basesequence is used for each cluster. Accordingly, it is possible toconsider a method in which different cyclic shift values are allocatedto multiple resources or different base sequences are allocated tomultiple resources. As a method of allocating a cyclic shift index toeach cluster, it is possible to consider a method in which a resourcecorresponding to each cluster is allocated using a cyclic shift indexthat has been defined to be signaled through higher layer signaling inthe LTE.

Embodiment 2 Definition of a Plurality of SRS Transmission Symbols in anSRS Transmission Subframe

The LTE-A supports multiple antennas or multilayer transmission based onthe multiple antennas by applying multiple power amplifiers/RF chains inuplink. Independent of or in parallel with such multi-antennatransmission, the LTE-A enables access to a plurality of UL componentscarriers and enables communication with a plurality of points through ULCoMP. Accordingly, when configuring a multi-antenna configuration, it ispossible to configure a plurality of SRS transmissions in order toguarantee multiplexing capacity, coverage, and measurement reliabilityin channel sounding for each individual antenna (or layer), for each ULcomponent carrier, or for each UL CoMP-based transmission point. Inorder to accomplish this, the present invention suggests that aplurality of SRS transmission symbols be defined in an uplink subframeof a UE (for example, an LTE-A UE). For ease of explanation, adescription will now be given of two configuration methods associatedwith depending on positions in a subframe when the number of SRStransmission symbols is defined to be 2.

FIG. 14 illustrates a first method for specifying two SRS transmissionsymbols in an uplink subframe according to an embodiment of the presentinvention. As shown in FIG. 14, a position of an SRS transmission symbolthat is additionally defined compared to the conventional LTE may bedefined to be located at a last transmission symbol (for example, OFDMor SC-FDMA symbol) of a first slot in a subframe that transmits an SRSof a corresponding UE. To accomplish this, shortened PUCCH formats thathave been used when an SRS is transmitted through two slots in theconventional LTE may be defined to be still used in the first slotaccording to the present invention.

FIG. 15 illustrates a second method for specifying two SRS transmissionsymbols in an uplink subframe according to an embodiment of the presentinvention. As shown in FIG. 14, a position of an SRS transmission symbolthat is additionally defined compared to the conventional LTE may bedefined to be located at a second last transmission symbol (for example,OFDM or SC-FDMA symbol) of a second slot in a subframe that transmits anSRS of a corresponding UE. This scheme has an advantage in that thefrequency of occurrences of power transition between an SRS transmissionsymbol and a data transmission symbol is the same as that when one SRStransmission symbol is defined in a subframe as in the conventional LTE.To accomplish this scheme, there is a need to additionally define ashortened PUCCH format in which 2 last transmission symbols arepunctured in an arbitrary slot based on the conventional LTE standard.The method of transmitting control information through a PUSCH of theconventional LTE uses rate matching of data and maps Rank Information(RI) to physical frequency resources of 4 transmission symbols in asubframe. For example, in the case of a normal CP, the RI is mapped tosecond and fifth transmission symbols in each slot of a subframe. Inthis case, the position of the fifth transmission symbol of the secondslot to which the RI is mapped overlaps the position of the additionalSRS transmission symbol suggested in the present invention. Accordingly,to apply this method, it is possible to consider an RI transmissionmethod which uses three transmission symbols, excluding the transmissionsymbol that is defined as the last symbol in the second slot, among thefour transmission symbols used for RI transmission. In addition, it ispossible to consider a method in which RI is mapped to physicalresources, starting from the first physical resource of the subframe, ina time-first manner or in which RI is mapped in a reversed order,starting from the last physical resource. In this case, the RI is mappedto transmission symbols, excluding or avoiding the transmission symbolto which an SRS is mapped, in a time-first manner. It is also possibleto consider a method in which the scheme of multiplexing CQI and datadefined in the conventional LTE is additionally applied to RI such thatRI is transmitted in a form of being multiplexed with data. In thiscase, RI is mapped to physical resources of a subframe in a time-firstmanner.

In the first and second suggested methods, it is possible to reduce theburden of having to individually define and signal a configurationparameter for an SRS transmission symbol for each slot. In addition, inorder to prevent the occurrence of transient operation of a poweramplifier (and/or signal amplifier) of each individual antenna atboundaries between SRS transmission symbols and data symbols, it ispossible to apply a method in which M SRS allocations required for acorresponding LTE-A UE are configured on an individual symbol instead ofbeing divided on a symbol by symbol basis and the M SRS allocations arerepeated in an SRS transmission symbol defined for each slot such thatpower allocated to each of the M SRSs is the sum of powers allocated totwo SRS transmission symbols. It is also possible to employ aconfiguration in which individual SRS bands are set at differentpositions for each slot while SRS resources are equally allocated toeach slot in two SRS transmission symbols as described above so that twouplink channel soundings are achieved in an arbitrary uplink subframe.The scheme in which the same SRS transmission bands are applied, thescheme in which different SRS transmission bands are applied, the schemein which two SRS transmission symbols are used, and the scheme in whichone SRS transmission symbol is used may be selectively appliedindividually or in combination depending on the situation of the UE.Indication information for configuring an SRS may be explicitly signaledusing an additionally defined RRC parameter or may be explicitly orimplicitly applied using L1/L2 control signaling or may be appliedimplicitly applied according to setting information of the transmissionmode or the state of the UE. The transmission mode information mayinclude information indicating whether or not MIMO transmission isperformed, information indicating whether or not non-contiguous RBallocation based transmission is performed, and the like.

As another method, it is possible to configure an overall multiplexingscheme in which, for two SRS transmission symbols in an arbitrary SRStransmission subframe, M SRSs that are to be transmitted by an arbitraryLTE-A UE are transmitted so as to be discriminated for each SRStransmission symbol by additionally applying a TDM scheme to theembodiments of the CDM, FDM, and CDM/FDM described in the presentinvention in order to reduce the time required for channel sounding forthe entire scheduling band. Here, code resources of SRS bands and/orcyclic shifts applied to the two SRS transmission symbols (optionallytogether with a base sequence index) may be specified independently ineach individual SRS transmission symbol. Here, as an additional method,the SRS transmission bands and the code resources may be intentionallyconfigured so as to be discriminated using different arbitrary resourcevalues. In consideration of signaling overhead of SRS-related RRCparameters that need to be additionally defined to accomplish thisscheme, the SRS transmission bands and the code resources applied to thetwo SRS transmission symbols may be commonly allocated (for example, theSRS transmission bands and the code resources may be configured equallyin terms of RRC parameters, control information, and code and frequencyresource allocation) and indication information used to discriminateresource allocation of individual SRSs in the two SRS transmissionsymbols may be additionally defined in control information in L1/L2control signaling or in an RRC parameter.

Embodiment 3 Precoded SRS Configuration

It is possible to consider precoded SRS transmission as a method forsecurely reducing the number of SRSs required for a corresponding UE andfor solving the problem of power amplifier on/off for SRS transmissionfor LTE-A UEs that support multiple antenna transmission throughmultiple power amplifiers/RF chains. According to this embodiment, evenin a situation in which a plurality of UE transmission antennas isconfigured, it is possible to define and use a single SRS resource inthe case of rank-1 MIMO transmission and to define and use a number ofSRS resources equal to a corresponding rank value in the case of higherrank MIMO transmission when performing Uplink Multiple Input MultipleOutput (UL MIMO). Precoding matrixes used for SRS precoding may beapplied according to precoding matrix index (PMI) information specifiedin the most recent uplink grant information. (Here, the same code bookas a code book defined for uplink data transmission is used as a codebook of PMI or Transmit Precoding Matrix Indication (TPMI) for SRStransmission.) Unlike this method, it is possible to consider a methodin which PMI information for SRS transmission is separately signaledthrough a series of L1/L2 control signaling including the case of ULgrant or UE-specific RRC signaling. In addition, it is possible toconfigure PMIs applied to all of an SRS or a DeModulation ReferenceSignal (DM-RS)/SRS as a code book of PMIs in a different form from aconventional data transmission code book for each layer (rank) numberand to define signaling information through UE-specific RRC signaling orL1/L2 control signaling indicating a PMI to be applied from among thePMIs of the code book. As another method, it is also possible to apply amethod in which, for uplink data using Transmit Diversity (TxD), one SRSand/or DM-RS resource is allocated using the PMIs described above in thesame manner as in the case of rank-1 for all of an SRS, a DM-RS, or anSRS/DM-RS and to transmit the corresponding RS based on the allocatedresource. Here, it is possible to apply a PMI(s) from among PMIs for asingle layer in a code book separately defined for RS transmission or adata transmission code book as described above. Taking intoconsideration the fact that TxD is associated with open-looptransmission, it is possible to consider a method in which the eNode Bindicates a separate PMI to the UE through UE-specific RRC signaling orL1/L2 control signaling. Unlike this method, according to the open-loopcharacteristics, it is also possible to apply a series of cycling,shifting, or permutation schemes through a transmission symbol or a slotlevel for a PMI used for a series of subsets or an entire set of singlelayer PMIs in a different manner in the time domain or in the frequencydomain. When the operation range of TxD is taken into consideration, thePMIs to be used may be selected and configured taking into considerationthe Cubit Metric/Peak to Average Power Ratio (CM/PAPR) characteristicsbased on single antenna transmission and may also be configured of PMIsof antenna selection format in order to prevent beam formation.

The methods which apply precoding to an SRS (or DM-RS) according to thisembodiment, together with methods which do not apply precoding, may beselectively applied to an arbitrary LTE-A UE. Here, as a criterion forselective application, it is possible to consider whether or not the UEis in a power-limited state, the UL MIMO transmission mode (rank orTxD/precoding), and the like. Detailed examples include a scheme inwhich a precoded SRS (or DM-RS) is transmitted for the rank 1 whichincludes or does not include TxD and a non-precoded SRS (or DM-RS) istransmitted for a higher rank. In another method, a precoded SRS (orDM-RS) is transmitted for the rank 1 and the rank 2 which include or donot include TxD and a non-precoded SRS (or DM-RS) is transmitted for ahigher rank. As another detailed embodiment, it is possible to considera scheme in which, for a DM-RS, precoding is applied to the rank 1 or toboth the rank 1 and the rank 2 for data transmission in a correspondingsubframe and a scheme independent from this scheme in which, for an SRS,precoding is performed with a PMI based on the rank 1 only in a limitedsituation or regardless of the channel state of the UE. As anothermethod, it is also consider a scheme in which orthogonal resourcesdiscriminated in the spatial domain are defined with PMIs for anarbitrary scheme among all types of SRS transmission resource allocationand multiplexing schemes. In this case, a method in which SRSs areprecoded with a series of rank-2 PMIs in a code book for datatransmission or a different code book for SRS transmission may beapplied selectively depending on the situation of the power-limited UEor may always be applied regardless of the channel condition of the UE.The PMIs used in this case are PMIs that provide a single antenna basedCM/PAPR and it is possible to define control information of L1/L2control signaling or UE-specific signaling for indicating a PMI to beused for SRS precoding. Unlike this method, a series of schemes such ascycling, shifting, or permutation schemes may be applied differently inthe time domain or the frequency domain through a slot level or atransmission symbol for a PMI set that is applied in an open-loop mannerbased on an arbitrary criterion according to the present invention.Here, the PMI set may be defined as all PMIs or as a series of subsets.

Embodiment 4 SRS Transmission Method in UL Carrier Aggregation Situation

In the case where a cell eNode B allocates multiple uplink componentcarriers to an arbitrary LTE-A UE, RRC parameters regardingconfiguration information such as the time of transmission and SRSresource allocation of each carrier among individual UL componentcarriers in association with SRS transmission may be acquired asindependent control information of each carrier through UE-specific RRCsignaling and each independent SRS transmission scheme may beimplemented in each UL component carrier. As a method for applying anassociation of inter-carrier SRS resource allocation and a transmissionscheme configuration, it is possible to apply a method in which acorresponding offset value between UL component carriers set at thetransmission start point are applied according to an explicit orimplicit rule in order to configure a subframe to be transmitted inunits of component carriers in a staggering manner while applying thesame SRS transmission period to each carrier in order to prevent anincrease in the CM/PAPR for uplink SRS transmission using multiplecomponent carriers.

Embodiment 5 SRS Transmission Method for Antenna Transmission Mode

The suggested methods for channel sounding according to theconfiguration of a plurality of uplink transmission antennas accordingto the present invention have been described mainly with reference tothe case where a signal is transmitted using all (physical) transmissionantennas (i.e., power is loaded to all (physical) transmission antennas)in an uplink multiple antenna transmission scheme that is applied toPUSCH or PUCCH transmission symbols excluding SRS symbol(s) in an SRStransmission subframe. However, there is a possibility that an antennaselection precoder is defined on a code book and is applied tocorresponding data transmission symbols or an uplink transmissiondiversity mode of an antenna selection or antenna group selection schemeof a closed-loop mode (for example, a long-term or short-term mode) isapplied in the case of, for example, uplink precoding as the technologyis applied to the system. Basically, it is possible to apply themultiple antenna channel sounding method suggested in the presentinvention in the case where such transmission modes are introduced. Inaddition, it is possible to apply methods for minimizing the occurrenceof turning on/off of a series of antenna power amplifiers and/or signalamplifiers between data transmission symbols and SRS transmissionsymbols when implementing detailed operations and procedures of themultiple antenna channel sounding method in a transmission mode havingsuch characteristics. In the following, the present invention suggestsmethods for applying channel sounding in the case where only specific(physical) antennas among all (physical) transmission antennas of the UEparticipate in uplink signal transmission.

Embodiment 5-1 Channel Sounding when Antenna Turn-on/Off Precoder isApplied

In the case where a UE performs uplink transmission using multipleantennas, antenna gain imbalance (AGI) may occur due to hand gripping ofthe user. In this case, transmission signals that are actually emittedfrom all or partial transmission antennas undergo a lost of 6 dB orgreater in terms of output power. When the eNode B has determined thatan AGI has occurred in a transmission antenna signal of a UE byobserving a signal (for example, a DM-RS or an SRS) transmitted from theUE, the eNode B may provide signaling to allow part of the transmissionantennas to turned off in order to prevent unnecessary power consumptionof the transmission antennas. On the other hand, there is a need for theeNode B to provide signaling to allow some transmission antennas to beturned on. To accomplish this, the eNode B may apply turn-on/offprecoders associated with antennas, in which an AGI has occurred, to acode book and may specify this application of the turn-on/off precodersthrough a series of UE-specific L1/L2 control signaling (for example,indication of a precoder in a DCI format in a UL grant). As anothermethod, it is possible to make an instruction to directly turn on/offoutput power of a transmission antenna, in which an AGI has occurred,through separate (or additional) UE-specific RRC signaling orUE-specific L1/L2 control signaling in a separate control channel DCIformat. In this suggestion, when a power control mechanism isindividually defined for each individual transmission antenna (or layer)or a power control mechanism is defined for each UE in a PUSCH powercontrol mechanism of the UE, the power control mechanism may be definedby multiplying an entire power control mechanism equation by a value of“1” as a signaling parameter in the “turn-on” case and by a value of “0”as a signaling parameter in the “turn-off” case. Of course, detailedequations, which can implement “turn-on/off” using the signalingparameter, may be included in the suggestions of the present invention.The following is a summary of methods for preventing the occurrence ofturn-on/off transition of power amplifiers and/or signal amplifiers atboundaries between data transmission symbols and SRS transmissionsymbols in the case where the precoding transmission mode having suchcharacteristics is applied to the data transmission symbols. The methodssuggested in the following description may also be applied as SRStransmission-related schemes when a series of antenna or antenna-groupselection precoders, which are not the antenna turn-on/off precodersintroduced due to causes such as AGI, are applied. First, an embodimentof the present invention is described below with reference to an antennaturn-on/off precoder.

Taking into consideration that an AGI occurs a semi-static manner,detailed configurations of SRS transmission (for example, configurationsassociated with SRS transmission timing, a detailed multiplexing scheme,an SRS band, and the like) are reconfigured at the time when theprecoder for antenna turn-on/off described above is applied or when itis applied to power control through signal in the eNode B and SRSsignals for antennas (or power amplifiers and signal amplifiers) whichare in a turn-on state from among all (physical) transmission antennasof the UE are multiplexed and transmitted in uplink in SRS transmissionsymbols according to an arbitrary scheme among the multiplexing schemessuggested in the present invention or according to a differentmultiplexing scheme. This may prevent the occurrence of turn-on/offtransition of power amplifiers and/or signal amplifiers at boundariesbetween data transmission symbols and SRS transmission symbols.

To allow a cell or an eNode B to monitor semi-static change of an AGIstate in a situation in which channel sounding limited to some of allantennas (or layers, power amplifiers or signal amplifiers) of the UE isimplemented as in the schemes described above as an AGI occurs, it isnecessary for the UE to perform channel sounding for all antennas atregular intervals to allow the cell or eNode B to measure change of theAGI state. To accomplish this, detailed SRS transmission configurationsmay be reconfigured through UE-specific RRC signaling so as to performchannel sounding in an entire or partial system band for all antennasduring a time duration sufficient for measurement at intervals of anappropriate period. UE-specific RRC signaling for reconfiguring thedetailed SRS transmission configurations may be performed in a periodicmanner or an event-triggered manner.

FIG. 16 illustrates an example in which a UE performs channel soundingthrough multiple antennas according to an embodiment of the presentinvention. In the example of FIG. 16, it is assumed that an AGI hasalready occurred such that some antennas (layers, power amplifiers, orsignal amplifiers) of the UE have been turned off and thus detailed SRStransmission configurations have been limited to (physical) transmissionantennas that are in a turn-on state. The antenna turn-off state can beapplied only to a specific frequency band or a specific (physical)channel (for example, a specific SRS transmission symbol). In the casewhere at least part of the transmission antennas have been set to aturn-off state, the eNode B needs to observe a signal transmitted fromthe UE in order to check whether or not the UE has escaped from the AGIsituation. To accomplish this, the UE may perform channel sounding byturning on/off the transmission antennas that have been set to aturn-off state in a periodic manner or an event-triggered manner. Thatis, when at least partial transmission antennas of the UE have been setto a turn-off state, the UE may perform channel sounding by temporarilyturning the transmission antennas on at intervals of a specific periodor according to a specific event while basically maintaining theturn-off state of the transmission antennas. For example, the UE mayperform channel sounding of a partial or entire system band for all(physical) transmission antennas by turning on all (or partial)(physical) transmission antennas of the UE during a duration B atintervals of a duration A. To accomplish this, a turn-on precoder may beapplied to an SRS transmission symbol during the duration B and aturn-off precoder may be applied to an SRS transmission symbol at asubsequent duration. The duration A corresponds to a channel soundingtransmission period applied to the antennas that are in a turn-on state.Here, the duration A may be set to be longer than the channel soundingtransmission period set for the antennas that are in a turn-on state.Specifically, the duration A may be set to a multiple of the channelsounding transmission period set for the antennas that are in a turn-onstate. In the case where channel sounding through the duration B isperformed in an event-triggered manner (for example, through L1/L2control signaling), the duration A may not be separatelydefined/signaled.

In combination with this method, it is possible to prevent theoccurrence of turn-on/off transition of power amplifiers and/or signalamplifiers at boundaries between data transmission symbols and SRStransmission symbols in a subframe by turning on all (or partial)(physical) transmission antennas through UE-specific RRC signaling,UE-specific L1/L2 control signaling or UE-specific UL grant PDCCHtransmission by a cell or an eNode B in the case where an antennaturn-off state has been achieved through a power control mechanism or byallowing precoders other than turn-on/off precoders to be used inassociation with the data transmission symbols in the case where theturn-on/off state of the transmission antennas have been temporarilytransitioned to a turn-on state for channel sounding (during theduration B). In this scheme, the durations A and B may be directlydefined as a time and may also be set in units of subframes, eachcorresponding to, for example, 1 ms, or in units of radio frames, eachcorresponding to, for example, 10 ms.

In another scheme, in the case where the eNode B desires to performmeasurement for checking whether or not the AGI situation of the UE haschanged in an event-triggered manner, the eNode B may make aninstruction to perform channel sound of all (or partial) (physical)transmission antennas during a preset duration or an explicitly orimplicitly signaled duration (for example, the duration B) through L1/L2control signaling (for example, through a UL grant PDCCH, a powercontrol PDCCH, or a dedicated PDCCH, or the like). In the case wherechannel sounding is performed during the duration B, each precoder for adata transmission symbol may be specified as a precoder other than anantenna turn-on/off precoder. This event-triggered signaling may also bespecified as UE-specific RRC signaling. This event-triggered scheme maybe implemented by specifying a precoder in a UL grant DCI format using aprecoder of a data transmission symbol while being tied withreconfiguration of detailed SRS transmission configurations.

In this scheme, in the case where precoding is applied to an SRS and aprecoder in a UL grant is specified not only using a precoder of a datatransmission symbol but also using a precoder of an SRS transmissionsymbol, antenna turn-on/off of (physical) transmission antennas thattransmit SRSs may be naturally implemented in a code book. Of course,the suggestions of this embodiment may also be applied in the case wherean SRS is precoded.

Embodiment 5-2 Channel Sounding in the Case where a TransmissionDiversity Scheme Based on Antenna (Group) Selection is Applied

All channel sounding schemes suggested in the above embodiment 5-1 maybe applied to this embodiment. This embodiment differs from theembodiment 5-1 in that UE-specific/cell-specific RRC control signalingfor SRS resetting (or reconfiguration) is performed in order to performchannel sounding of corresponding (physical) transmission antennas in asituation in which the antennas (or power amplifiers or signalamplifiers) are in a turn-off state when performing detailed SRStransmission configuration at the time when antenna selectionspecification for a series of AGIs or other specific channel informationis performed through UE-specific RRC signaling, a UE-specific UL grantPDCCH, or a different type of UE-specific dedicated PDCCH. In addition,the same schemes as the detailed schemes of the embodiment 5-1 may beapplied to parameters that are signaled through a power controlmechanism that is individually defined for a (physical) transmissionantenna or through a power control mechanism of the UE in associationwith antenna turn-on/off on the UE.

Embodiment 5-3 Channel Sounding when Dynamic Antenna Selection Precoderis Applied

It is possible to apply any of the detailed schemes for SRS transmissionsuggested in the embodiment 5-1, taking into consideration that basicSRS setting is performed in a semi-static manner in the case where anantenna selection precoder is applied in a dynamic or semi-staticmanner. In addition, it is possible to apply the suggested schemes ofthe embodiment 5-1, in which the precoded SRS is applied, and also toconsider a scheme in which an event-triggered-based SRS is used.

Embodiment 5-4 Channel Sounding when an Antenna or Antenna-GroupSelection Based Transmission Mode (which can be Represented as a Type ofTransmission Diversity Scheme) is Applied

Basically, it is possible to apply any of the schemes suggested in theembodiment 5-1 in the case where closed-loop or open-loop antennaselection is implemented using one or more power amplifiers and(physical) transmission antennas from among power amplifiers and(physical) transmission antennas provided in an arbitrary UE in adynamic or semi-static manner (for example, using UE-specific RRCsetting (signaling)). Here, each (physical) transmission antenna may befixedly connected to a specific power amplifier or may be switchablyconnected to outputs of a series of power amplifiers. The following is amore detailed description of a method for minimizing the occurrence oftransition of power amplifiers and transmission antennas at boundariesof data transmission symbols and SRS transmission symbols when SRStransmission is performed and minimizing the impact (or influence) ofthe transition of the power amplifiers and the transmission antennas.

In a situation in which antenna or antenna group selection is performedwhen an antenna or antenna group selection based transmission mode(which can be represented as a type of transmission diversity scheme) isapplied, the eNode B may reconfigure detailed SRS transmissionconfigurations (for example, SRS transmission timing, detailedmultiplexing schemes, SRS band, and the like) and signal reconfiguredconfigurations to the UE at the time when the transmission mode isapplied. On the other hand, the UE multiplexes and transmits SRSs forantennas (or power amplifiers and signal amplifiers) which are used fordata transmission from among all (physical) transmission antennas of theUE in uplink in SRS transmission symbols according to an arbitraryscheme among the multiplexing schemes suggested in the present inventionor according to a different multiplexing scheme. This may prevent theoccurrence of turn-on/off transition of power amplifiers and/or signalamplifiers at boundaries between data transmission symbols and SRStransmission symbols. In this SRS configuration scheme, it is possibleto especially match SRS settings (configurations) in order to preventthe transition of power amplifiers and transmission antennas attransmission symbol boundaries in the case where a special configurationof a single antenna and power amplifier has been set, as when the UEincludes 2 transmission power amplifiers for 4 (physical) transmissionantennas, and in the case where transmission (physical) antennas ofpower amplifier output terminals are switched according to the specialconfiguration.

In a situation in which channel sounding limited to partial ones of the(physical) transmission antennas (or layers or power amplifiers orsignal amplifiers) of the UE is implemented, the UE performs channelsounding on all (or partial) antennas at regular intervals (or in aperiodic manner) to allow the eNode B to measure channel changes ofindividual (physical) transmission antennas of the UE in order to allowthe eNode B to select antennas or antenna groups from the transmissionantennas (or layers or power amplifiers or signal amplifiers) of the UE.To accomplish this, it is possible to perform selection of antennas orantenna groups upon data transmission through UE-specific RRC signalingat regular intervals so as to perform channel sounding of an entire orpartial system band of all (or partial) antennas during a durationsufficient for measurement at intervals of an appropriate period and toperform reconfiguration of detailed SRS transmission configurationssuitable for the selection of antennas or antenna groups.

The example of FIG. 16 illustrated in association with the embodiment5-1 may also be applied to perform channel sounding when antennaselection is applied according to this embodiment. In this case, it canbe assumed that in the example of FIG. 16 that detailed SRS transmissionconfigurations have been limited to (physical) transmission antennasthat are in a turn-on state when specific transmission antennas are usedin the case where antenna or antenna group selection for a series ofdata transmissions is applied. In this case, the UE may perform channelsounding by turning on/off the transmission antennas that have been setto a turn-off state in a periodic manner or an event-triggered manner.That is, when at least partial transmission antennas of the UE have beenset to a turn-off state, the UE may perform channel sounding bytemporarily turning the transmission antennas on at intervals of aspecific period or according to a specific event while basicallymaintaining the turn-off state of the transmission antennas. Forexample, the UE may perform channel sounding of a partial or entiresystem band for all (physical) transmission antennas by turning on all(or partial) (physical) transmission antennas of the UE during aduration B at intervals of a duration A. To accomplish this, a turn-onprecoder may be applied to an SRS transmission symbol during theduration B and a turn-off precoder may be applied to an SRS transmissionsymbol at a subsequent duration. The duration A corresponds to a channelsounding transmission period applied to the antennas that are in aturn-on state. Here, the duration A may be set to be longer than thechannel sounding transmission period set for the antennas that are in aturn-on state. Specifically, the duration A may be set to a multiple ofthe channel sounding transmission period set for the antennas that arein a turn-on state. In the case where channel sounding through theduration B is performed in an event-triggered manner (for example,through L1/L2 control signaling), the duration A may not be separatelydefined/signaled.

In combination with this method, it is possible to apply a method oftemporarily releasing the selection mode to allow all (physical)transmission antennas of the UE to be applied for transmission of datatransmission symbols. It is also possible to prevent the occurrence ofturn-on/off transition of power amplifiers and/or signal amplifiers atboundaries between data transmission symbols and SRS transmissionsymbols in a subframe by turning on all (or partial) (physical)transmission antennas through UE-specific RRC signaling, UE-specificL1/L2 control signaling or UE-specific UL grant PDCCH transmission by acell or an eNode B in the case where an antenna turn-off state has beenachieved through a power control mechanism. In this scheme, thedurations A and B may be directly defined as a time and may also be setin units of subframes, each corresponding to, for example, 1 ms, or inunits of radio frames, each corresponding to, for example, 10 ms.

In another scheme, in the case where the eNode B desires to performmeasurement for checking whether or not channel states of all (physical)transmission antennas of the UE have changed in an event-triggeredmanner, the eNode B may make an instruction to perform channel sound ofall (or partial) (physical) transmission antennas during a presetduration or an explicitly or implicitly signaled duration (for example,the duration B) through L1/L2 control signaling (for example, through aUL grant PDCCH, a power control PDCCH, or a dedicated PDCCH, or thelike). In the case where channel sounding is performed during theduration B, each precoder for a data transmission symbol may bespecified as a precoder other than an antenna turn-on/off precoder. Thisevent-triggered signaling may also be specified as UE-specific RRCsignaling. This event-triggered scheme may be implemented by specifyinga precoder in a UI grant DCI format using a precoder of a datatransmission symbol while being tied with reconfiguration of detailedSRS transmission configurations.

In this scheme, in the case where precoding is applied to an SRS and aprecoder in a UL grant is specified not only using a precoder of a datatransmission symbol but also using a precoder of an SRS transmissionsymbol, antenna turn-on/off of (physical) transmission antennas thattransmit SRSs may be naturally implemented in a code book. Of course,the suggestions of this embodiment may also be applied in the case wherean SRS is precoded.

A variety of information for channel sounding may be dynamically ornon-dynamically signaled in the above embodiment 1-5 of the presentinvention. For example, in the present invention, information forchannel sounding may be signaled in a UE-specific or a UE-group-specificmanner through L1/L2 control signaling. More specifically, informationfor channel sounding may be transmitted from the eNode B (or relay) tothe UE through a conventional PDCCH defined in the LTE system, aseparately defined PDCCH, or through a control channel separatelydefined for signaling the information for channel sounding. In the casewhere the information for channel sounding is transmitted from the eNodeB (or relay) to the UE through a separately defined PDCCH, an RNTI foran SRS may be defined or a DCI format may be separately defined. L1/L2control signaling for an SRS may be performed at a preset time (forexample, a period or offset) or may be performed in an event-triggeredmanner. In the case of a carrier aggregation system, L1/L2 controlsignal for channel sounding may be performed for each downlink componentcarrier set for the UE or may be performed only through a specificdownlink component carrier (for example, through an anchor or primary DLcomponent carrier). In this case, anchor or primary component carriersmay be set one by one for each downlink component carrier group.

The information for channel sounding includes, but not limited to,information for newly configuring (or initiating) or releasing an SRS.For example, in the case where the eNode B has transmitted an L1/L2control signaling signal (for example, a PDCCH) having a specificformat/content (for example, a specific indicator) to the UE, the UE maystart or release SRS transmission after a preset time has elapsed afterthe signaling is performed or after the UE has received the L1/L2control signaling signal. The information for channel sounding mayinclude configuration information (SRS transmission configurationinformation) required for SRS transmission (for example, an offset, aperiod, and the like). When the UE has newly received the SRStransmission configuration information through the L1/L2 controlsignaling, the UE may override (or overwrite) preset configurationinformation with the newly received SRS transmission configurationinformation. Alternatively, while maintaining the preset configurationinformation, the UE may perform channel sounding using the newlyreceived SRS transmission configuration information only during a presettime or during a duration in which a preset condition is satisfied. Theinformation transmitted through the SRS transmission configurationinformation may include entire or partial information required toperform channel sounding. The detailed content included in the SRStransmission configuration information may set in various mannersdepending on the type of signaling, the time of signaling, the cause ofsignaling, and the like. Specifically, the SRS transmissionconfiguration information may include, but not limited to, at least partof the SRS configuration parameters of the LTE described above withreference to FIG. 5 and various parameters that are newly defined or arerequired to implement the embodiment 1-5.

FIG. 17 illustrates an eNode B and a UE to which the embodiments of thepresent invention may be applied.

As shown in FIG. 17, a wireless communication system includes a BaseStation (BS) (or eNode B) 110 and a User Equipment (UE) 120. Indownlink, a transmitter is a part of the BS 110 and a receiver is a partof the UE 120. In uplink, a transmitter is a part of the UE 120 and areceiver is a part of the BS 110. The BS 110 includes a processor 112, amemory 114, and a Radio Frequency (RF) unit 116. The processor 112 maybe constructed so as to implement the procedures and/or methodssuggested in the present invention. The memory 114 is connected to theprocessor 112 and stores various information associated with operationsof the processor 112. The RF unit 116 is connected to the processor 112and transmits or receives a wireless signal. The UE 120 includes aprocessor 122, a memory 124, and an RF unit 126. The processor 122 maybe constructed so as to implement the procedures and/or methodssuggested in the present invention. The memory 124 is connected to theprocessor 122 and stores various information associated with operationsof the processor 122. The RF unit 126 is connected to the processor 122and transmits or receives a wireless signal. The BS 110 and/or the UE120 may include a single antenna or multiple antennas.

The above embodiments are provided by combining components and featuresof the present invention in specific forms. The components or featuresof the present invention should be considered optional unless explicitlystated otherwise. The components or features may be implemented withoutbeing combined with other components or features. The embodiments of thepresent invention may also be provided by combining some of thecomponents and/or features. The order of the operations described abovein the embodiments of the present invention may be changed. Somecomponents or features of one embodiment may be included in anotherembodiment or may be replaced with corresponding components or featuresof another embodiment. It will be apparent that claims which are notexplicitly dependent on each other can be combined to provide anembodiment or new claims can be added through amendment after thisapplication is filed.

The embodiments of the present invention have been described focusingmainly on the data communication relationship between a UE (or terminal)and a Base Station (BS) (or eNode B). Specific operations which havebeen described as being performed by the BS may also be performed by anupper node as needed. That is, it will be apparent to those skilled inthe art that the BS or any other network node may perform variousoperations for communication with terminals in a network including anumber of network nodes including BSs. The term “base station (BS)” maybe replaced with another term such as “fixed station”, “Node B”, “eNodeB (eNB)”, or “access point”. The term “terminal” may also be replacedwith another term such as “user equipment (UE)”, “mobile station (MS)”,or “mobile subscriber station (MSS)”.

The embodiments of the present invention can be implemented by hardware,firmware, software, or any combination thereof. In the case where thepresent invention is implemented by hardware, an embodiment of thepresent invention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, or the like.

In the case where the present invention is implemented by firmware orsoftware, the embodiments of the present invention may be implemented inthe form of modules, processes, functions, or the like which perform thefeatures or operations described above. Software code can be stored in amemory unit so as to be executed by a processor. The memory unit may belocated inside or outside the processor and can communicate data withthe processor through a variety of known means.

Those skilled in the art will appreciate that the present invention maybe embodied in other specific forms than those set forth herein withoutdeparting from the spirit of the present invention. The abovedescription is therefore to be construed in all aspects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all changes comingwithin the equivalency range of the invention are intended to beembraced in the scope of the invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a wireless communication system.Specifically, the present invention is applicable to a channel soundingmethod using a plurality of antennas and an apparatus for the same.

1. A method of transmitting sounding reference signals at a userequipment UE in a wireless communication system, the method comprising:generating sounding reference sequences for multiple antenna ports, eachsounding reference sequence being defined using a base sequence numberand a cyclic shift value; mapping each sounding reference sequence toresource elements of a corresponding antenna port on a single carrierfrequency division multiple access SC-FDMA symbol of a subframe; andtransmitting the sounding reference sequences for the multiple antennaports within the SC-FDMA symbol of the subframe, wherein one of cyclicshift values for the multiple antenna ports is specified using asignaled value, and one or more remaining cyclic shift values for themultiple antenna ports are specified using one or more offsets and thesignaled value.
 2. The method of claim 1, wherein sounding referencesequences of all of the multiple antenna ports are mapped to the sameset of every two resource elements.
 3. The method of claim 1, whereinsounding reference sequences for a first group of antenna ports aremapped to a set of every two resource elements, and sounding referencesequences for a second group of antenna ports are mapped to another setof every two resource elements.
 4. The method of claim 1, wherein theSC-FDMA symbol is a last SC-FDMA symbol of the subframe.
 5. A method ofprocessing sounding reference signals at a base station BS in a wirelesscommunication system, the method comprising: receiving soundingreference sequences for multiple antenna ports of a user equipment UE onresource elements of a single carrier frequency division multiple accessSC-FDMA symbol of a subframe, each sounding reference sequence beingdefined using a base sequence number and a cyclic shift value; andde-mapping each sounding reference sequence from the resource elementsof a corresponding antenna port on the SC-FDMA symbol of the subframe,wherein one of cyclic shift values for the multiple antenna ports isspecified using a signaled value, and one or more remaining cyclic shiftvalues for the multiple antenna ports are specified using one or moreoffsets and the signaled value.
 6. The method of claim 5, whereinsounding reference sequences of all of the multiple antenna ports aremapped to the same set of every two resource elements.
 7. The method ofclaim 5, wherein sounding reference sequences for a first group ofantenna ports are mapped to a set of every two resource elements, andsounding reference sequences for a second group of antenna ports aremapped to another set of every two resource elements.
 8. The method ofclaim 5, wherein the SC-FDMA symbol is a last SC-FDMA symbol of thesubframe.
 9. A user equipment UE used for a wireless communicationsystem, the UE comprising: a radio frequency (RF) unit; and a processor,wherein the processor is configured to generate sounding referencesequences for multiple antenna ports, each sounding reference sequencebeing defined using a base sequence number and a cyclic shift value, mapeach sounding reference sequence to resource elements of a correspondingantenna port on a single carrier frequency division multiple accessSC-FDMA symbol of a subframe, and transmit the sounding referencesequences for the multiple antenna ports within the SC-FDMA symbol ofthe subframe, wherein one of cyclic shift values for the multipleantenna ports is specified using a signaled value, and one or moreremaining cyclic shift values for the multiple antenna ports arespecified using one or more offsets and the explicitly signaled value.10. The UE of claim 9, wherein sounding reference sequences of all ofthe multiple antenna ports are mapped to the same set of every tworesource elements.
 11. The UE of claim 9, wherein sounding referencesequences for a first group of antenna ports are mapped to a set ofevery two resource elements, and sounding reference sequences for asecond group of antenna ports are mapped to another set of every tworesource elements.
 12. The UE of claim 9, wherein the SC-FDMA symbol isa last SC-FDMA symbol of the subframe.
 13. A base station BS used for awireless communication system, the communication apparatus comprising: aradio frequency (RF) unit; and a processor, wherein the processor isconfigured to receive sounding reference sequences for multiple antennaports of a user equipment UE on resource elements of a single carrierfrequency division multiple access (SC-FDMA) symbol of a subframe, eachsounding reference sequence being defined using a base sequence numberand a cyclic shift value, and de-map each sounding reference sequencefrom the resource elements of a corresponding antenna port on theSC-FDMA symbol of the subframe, wherein one of cyclic shift values forthe multiple antennas ports is specified using a signaled value, and oneor more remaining cyclic shift values for the multiple antenna ports arespecified using one or more offsets and the signaled value.
 14. The BSof claim 13, wherein sounding reference sequences of all of the multipleantenna ports are mapped to the same set of every two resource elements.15. The BS of claim 13, wherein sounding reference sequences for a firstgroup of antenna ports are mapped to a set of every two resourceelements, and sounding reference sequences for a second group of antennaports are mapped to another set of every two resource elements.
 16. TheBS of claim 13, wherein the SC-FDMA symbol is a last SC-FDMA symbol ofthe subframe.